Cosmologist

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Pint of science is quite simply a wonderful idea. It combines two of my favourite things. Science. And the pub. What could be better?

Basically its a bunch of scientists excitedly sharing cutting edge research, in a pub! The audience can enjoy a beer with their science.

This year some wonderful people from Queen Mary (including cosmology PhD superstar Sophia Goldberg) have organised three nights of incredible talks in an amazing Spitalfields venue, from Monday 19th May – Wednesday 21st May. Topics include everything from Darwinian machine learning concepts, to awe-inspiring images of Saturn from the Cassini satellite. I’m talking cosmology on the Tuesday.

I’m pleased to say I’m visiting the University of Helsinki for a month. Thanks to Kari Enqvist and Sami Nurmi for the invitation.

So far I’ve been here just over a week, and am really enjoying it. Helsinki is a beautiful city (as the picture proves), and the cosmology group in the institute of physics is really great. All in all a wonderful place to get some work done.

Hopefully the visit will result in some joint publications with the guys in Helsinki, so watch this space….

I found it hard to write things in a simple way, and only got to set the scene for the research I do in the word limit available. Hopefully it’s helpful for people starting to think about cosmology for the first time. And I hope to add another article actually about cosmology research in Queen Mary soon….

After some friends seemed interested, having seen it in the news, I posted a short explanation of the recent announcement from the BICEP team on facebook. They have seen B-mode polarisation of the CMB, and hence found evidence for gravitational waves being present in the early universe. I don’t think all the explanations out there in the news are that helpful, so I thought I’d reproduce my short one here in case anyone stumbles on it and is interested. Here’s what was discovered:

The BICEP team released analysis of the data they have been taking over the past few years. They observe the Cosmic Microwave Background (CMB) (wikipedia it for more info) — radiation that has propagated to us since the time of “last scattering” not long (in cosmological terms ~400,000 years) after the big bang and is now microwave radiation. In particular they can look at how this radiation is polarised. The CMB looks almost the same in every direction we look, reflecting the fact that the early universe was extremely smooth. The small differences are mainly the result of there being small differences in the distribution of matter in the early universe. Crucially, however, part of the difference could also be the result of waves in the gravitational field itself being present at the time of last scattering. Polarisation data helps scientists separate out the effects of the matter density fluctuations from the effects of the gravitational waves. The BICEP team are the first to present strong evidence that gravitational waves were indeed present in the early universe at the time of last scattering. Such waves are an important prediction of Einstein’s theory that have not yet been directly detected (by a gravitational wave telescope for example). Moreover, such waves are thought to be produced (along with the density fluctuations), during a much earlier more speculative phase of the universe’s evolution called “inflation” (this would have taken place when the universe was only a fraction of a second old). So yesterday’s discovery is also further evidence for inflation. I work on inflation so I’m pretty happy about that! Go BICEP!

In previous posts I’ve highlighted that I am engaged in developing new tools to take an inflationary model and calculate its observational consequences. In a recent paper, together with John Ellis and Nick Mavromatos at Kings, I applied some of these techniques to a particular model of inflation: the Wess-Zumino model.

This model is realistic, in the sense that it has particle physics motivation, and necessarily has two fields involved in the dynamics, as well as having one free parameter. This means that for every value of the free parameter there are a set of initial conditions, which lie on a one dimensional line in the two dimensional field space, that give rise to the observed number of e-folds of inflation. Every point on this line gives a different prediction for the observational parameters that are constrained by data.

In our paper we attempted to give a fairly complete study of the different values of the observational parameters that can arise for this model. We found some interesting things, like the fact that there are values of the free model parameter for which the multi-field dynamics are essential to allow any initial conditions to be consistent with observations, and that for these cases enhanced values of non-Gaussianity can arise. We also tried to interpret this model in a probabilistic manner, asking not just what observable signatures are possible, but also what are likely given some distribution on the space of initial conditions.

All in all it was an interesting paper to work on, and nice to be using some of the numerical tools I’ve been helping to develop. We hope to release some of these tools for others to use in the near future, so watch this space!

Earlier this year, the first, long awaited, analysis of cosmological data from the Planck satellite was released. In a series of papers, the Planck team told us the outcome of the years the satellite spent observing the cosmic microwave background (CMB). In particular, they greatly improved constraints on the statistical properties of primordial perturbations. These perturbations imprint themselves on the CMB as temperature fluctuations. To those of us who study inflation, which is thought to produce these perturbations, and who research methods to better predict the statistics a given model of inflation gives rise to, it was a disappointment to learn that there was no detection confirming the statistics are non-Gaussian. Instead the bounds on how much the three-point correlation function, the first non-Gaussian statistic, can vary from zero were considerably tightened. This is summarized by the constraints on the parameter which parametrises the amplitude of the three-point function: . We see that is consistent with zero.

The simplest models of inflation — one field with standard kinetic energy and a smooth potential — predict , while models with more than one field can produce a much larger that would have been detected by Planck. It has been argued, therefore, that the Planck results for , in combination with results on other parameters, support single field models. In a new paper, myself and collaborators Joe Elliston and Reza Tavakol argue something slightly different: the results tell us that there is no pressure to consider multi-field models, but that such models are still consistent for large regions of their feasible initial condition and parameter spaces. Moreover, there are other reasons that might lead us to consider multi-field models rather than single field ones, such as asking where in fundamental physics the inflaton field comes from, and whether it is likely that just one field contribute to inflation in that context. Continue reading →

Facultimedia.com is an ambitious new website which aims to present recent research through short videos presented by the academics responsible. It also features more introductory videos talking about the general area of the research. Its not completely clear what their end goal is and how the website will develop, but I for one think the general idea is extremely worthwhile and interesting (update: they have explained their goals in the comments below!).

This week I got filmed by them, and produced one introductory video on cosmology and inflation, and one more technical one (though still accessible to the public I hope) on transport techniques for inflationary observables (see the last news item).

It was an interesting experience, and made me realise how hard just talking for a few minutes at a camera can be. I wish I’d done a little more preparation or scripted it, or just practiced it a few times! (only time for one take). But I hope there is something of interest in the videos, and I’ll certainly learn from the experience.